Sr and Mg were doped at La- and Ru-sites of perovskite oxide LaRuO3, respectively, to enhance electrical conductivity and catalytic property as a cathode material for a low temperature solid oxide fuel cell. Crystal structure and particle morphology of La0.6Sr0.4Ru1-xMgxO3-delta powders (shorten as LSRM) and electrical conductivity of sintered LSRM were studied. LSRM powders (x = 0-0.6) were prepared by co-precipitation method using metal nitrate solutions and ammonium carbonate solution. The freeze-dried powders were heated at 1273 K in air to form LSRM solid solution of orthorhombic structure. The true densities and particle sizes of LSRM solid solution, where valence of Ru was estimated to be 3+, decreased with increasing Mg content. The electrical conductivity of LSRM at x = 0-0.3 was almost independent of temperature and was in a range of 19-360 S cm(-1) at 1073 K. Hole conduction contributed to the high electrical conductivities. LSRM at x = 0.4 and 0.5 was a mixed conductor of oxide ions and holes, and showed a conductivity of 11 S cm(-1) at 1073 K in air. This conductivity decreased at a lower oxygen pressure and reached a constant value below 10 Pa of oxygen pressure. (C) 2010 Elsevier BM. All rights reserved.